I seem to have run across a dispute about whether or not the various pulleys involved with a timing belt should spin freely or not.
For example, in this video the anonymous Internet expert says that a good t-belt pulley spins freely. Also, @Ben from this site says the same.
However, I ran across other opinions stating the exact opposite:
pulleys in good condition will stop very shortly after you spin them by hand. New pulleys will stop immediately. Natural friction of the grease inside the bearing caps are what slows down rotation.
What I've found the most convincing so far is this video in which a guy presses brand new bearings into his t-belt idler pulley and gives it a little spin and it stops very quickly.